This invention relates to the melting of glass and, in particular, to the charging and melting of glass batch materials in a regenerative or recuperative furnace that is provided with means for heating the glass batch materials from above in order to melt them for the production of glass in large commercial quantities, particularly for the production of flat glass. The invention relates particularly to the treatment of unmelted glass batch materials that have been charged to the furnace in order to improve melting efficiency of the furnace.
It is well known that glass batch materials used to produce sodalime-silica glass may be melted in large commercial quantities on the order of from 100 to 700 tons per day in regenerative, tank-type furnaces. It has also been known to melt glass batch materials in substantial quantities in recuperative, tank-type furnaces. In the practice of making glass in such furnaces, glass batch materials have long been fed to the furnaces by continuous feeders or by intermittent feeders. Continuous batch feeders, as well as intermittent or periodic batch feeders, are shown and described in many U.S. patents. They may be charged continuously using a blanket feeder of the type described in the following U.S. Pat. Nos. 1,623,057 and 2,624,475 which show devices for feeding a single layer of batch; 2,114,545 and 2,711,837 which show continuous belt devices for feeding two layers -- one of cullet and one of batch over the cullet; 2,829,784 which shows a rotating paddle device for feeding two layers -- one of cullet and one of batch; and 2,773,611 which shows a device for feeding three layers of batch and cullet.
Alternatively, glass batch materials may be charged using intermittent push feeders such as described in the following U.S. Pat. Nos. 1,483,278; 1,913,665; 1,916,262; 1,917,247; 1,953,221; 2,281,050; 2,284,398; 2,284,420; 2,471,336; 2,556,467; 2,815,135 and 3,193,119 which show devices for feeding continuous transverse logs of batch; 2,831,567 which shows side wall pushers; 2,934,221 which shows a device for feeding divided logs and 509,930; 1,928,016 and 1,941,897 which show devices for feeding two or more streams of batch intermittently to a furnace.
When glass batch materials are fed to a furnace, whether by intermittent feeders or continuous feeders, the glass batch forms as a substantially continuous layer or blanket on top of molten glass near the charging or fill end of the furnace. When intermittent feeders are employed, there is a variation in depth of the layer of batch corresponding to the intermittent nature of feeding. There are peaks corresponding to individual charging or feeding steps and valleys or depressions between the peaks corresponding to the time between successive feeding steps when glass batch materials are not charged.
When the glass batch materials are fed to a furnace continuously, a uniform batch blanket is generally formed on top of the molten glass with the blanket having generally uniform thickness and presenting a relatively flat, upper surface to overhead heating flames. With either method of feeding glass batch, the top surface of batch blanket is flatter than would be desired. Generally, a blanket or layer of batch does not have depressions of sufficient depth into which molten glass can run as the glass batch materials on the surface melt. Such a runnage of molten glass would be useful to continuously expose new unmelted batch materials to overhead flames for melting.
It has long been an objective of glassmakers to provide for more efficient melting of glass batch materials by breaking up the relatively flat, continuous surfaces of batch blankets near the feed ends of glassmaking furnaces. For example, U.S. Pat. No. 3,074,568 illustrates an attempt to provide furrows or the like in glass batch blankets resulting from continuous charging or feeding of glass batch to a glassmaking furnace. In U.S. Pat. No. 2,533,826 there is provided a rabble in the charging end of the glassmaking furnace to periodically move down through a layer of glass batch materials into the molten glass beneath it and to enfold the glass batch materials with molten glass. There have also been a number of schemes in which the glass batch is periodically pressed downward into the glass in order to provide depressions in the upper surface of a floating layer of batch.
The devices which have been employed in the past which press downwardly on a relatively thick layer of glass batch materials immediately after they have been fed or charged to a glassmaking furnace suffer from a common deficiency. The glass batch materials which have been pressed or compacted downwardly at a particular location into the molten glass beneath them rise again upon withdrawal of the compacting or stamping device due to the buoyancy of the glass batch, and the depressions that are so formed are short lived.
The present invention provides an improved apparatus and method for providing depressions in a layer of glass batch materials that have just been charged or fed to a glassmaking furnace.